Drop on demand inkjet technology for producing printed images has been employed in products such as printers, multifunction products, plotters, and facsimile machines. Generally, an ink image is formed by selectively ejecting ink drops from a plurality of ejectors or inkjets, which are arranged in an array within a printhead, onto an image receiving substrate. For example, the image receiving substrate may be moved relative to the printhead and the inkjets may be controlled to eject ink drops through nozzles formed in the printhead at appropriate times. The timing of the inkjet activation is performed by a printhead controller, which generates firing signals that activate the inkjets to eject ink. The ink ejected from the inkjets is liquid ink, such as aqueous, solvent, oil based, curable ink, or the like. The ink is stored in containers installed in the printer and the containers are fluidly connected to the printheads. Alternatively, the ink may be loaded in a solid or a gel form and delivered to a melting device, which heats the ink to generate liquid ink that is supplied to a printhead.
The ink by an inkjet travels through an air gap between the printhead face and the image receiving substrate. The greater the distance between the printhead face and the image receiving member, the greater the expelled ink drop speed and consistency required to travel this distance and land on the substrate at the position intended for the ejected ink drops. Inkjet printers that print images on precut sheets of print media are referred to as cut sheet inkjet printers. Cut sheet inkjet printers strip media sheets from a supply of media sheets stacked on an input tray. A media conveyer transports each stripped media sheet through a print zone of the printer where the printheads are located. The inkjets of the printheads eject ink onto the print media as the media conveyer transports the print media through the print zone. After receiving ink from the inkjets, the media conveyer transports the stripped media sheet to an output tray. Once received by the output tray the media sheets are collected by a user or received by another printing system for further processing. In continuous sheet printers, media is pulled from a rotating roll and actuators driving rollers propel the sheet through the printer past the printheads and post-printing processing equipment to a take-up roll.
In cut-sheet printers, some media sheets stripped from the input tray may include creases and other imperfections. Additionally, water from the ink landing on a media sheet can cause a portion of the sheet to curl, which increase the sheet's height above the transport. In continuous sheet printers, the risk of sheet curl is also present. If a portion of a media sheet actually touches the face of a printhead, a significant danger exists of disrupting the complete functioning of one or more of the jets. This disruption might be either temporary or permanent but in either case the image quality suffers significantly. Therefore, protecting printheads in cut sheet and continuous sheet printers from media passing by the printheads would be useful.